The invention relates to the correction of presbyopia.
The said defect is a loss of accommodation affecting the entire population, starting from the age of about forty. It is manifested in a reduction in the acuity of near vision and is generally corrected by wearing positive convergent glasses that allow images that formerly formed behind the retina to be focussed on the retina.
Emmetropic individuals often feel, however, that having to wear spectacles of that type on a permanent basis is a nuisance and unsightly.
In order to avoid those disadvantages, it is known for the presbyopia to be treated surgically by carrying out remodelling of the cornea with the aid of a laser beam apparatus known by the commercial designation Excimer. The remodelling can be performed on the surface or lower down within the corneal stroma, a technique known by the name of Lasik. However, with living tissue, the scarring of which is unpredictable, it is difficult to produce very accurate curvatures in very small areas. The results of these techniques are the subject of much debate.
More recently, another means of surgically treating presbyopia has been proposed, by implanting on the sclera, in line with the ciliary body, segments that have the function of retensioning the zonule.
It is also known for aphakic eyes to be fitted with posterior chamber implants which are placed either within the capsular sac or in the sulcus and the optical portion of which is termed multifocal because it is treated to allow near vision and vision that is intermediate between near vision (30 cm) and distance vision (from 3 m).
U.S. Pat. No. 4,955,902 furthermore discloses an ocular implant provided for correcting substantial myopia in an eye having an off-center pupil. The implant is positioned in the anterior chamber of the eye; it comprises an optical portion having a concave face and a thick external periphery matched to the correction of the myopia and a dissymmetrical haptic portion allowing the said optical portion to be so positioned that its focal axis is arranged off-centre with respect to the geometric axis of the eye, towards the nasal side.
However, to the knowledge of the Applicant, no-one has until now envisaged or suggested treating presbyopia in emmetropic phakic eyes y means of implants arranged in the anterior chamber or posterior chamber, in the manner of implants currently used for correcting ametropias such as myopia, astigmatism or hypermetropia.
The aim of the present invention is to propose such an implant for an emmetropic phakic eye.
According to the invention, this implant, which comprises an optical portion and a haptic portion arranged to position the focal axis of the said optical portion off-centre with respect to the geometric axis of the eye, towards the nasal side, is characterised in that it is provided for insertion into a phakic eye to correct presbyopia, its optical portion having, at least in its central region, a multifocal treatment constituting an addition of from +1 to +3.5 dioptres, and its haptic portion ensuring that the optical axis of the central portion is arranged from 0 to 0.75 mm off-centre when the implant is in position in the eye.